Background: Venous insufficiency is the most common culprit behind free flap failure. Considering that the dependent position of the lower extremity predisposes to venous congestion at baseline, we investigated the effect of a second venous anastomosis on free flap outcomes in lower extremity trauma reconstruction.

Conclusion: While two venous anastomoses reduced the overall risk of complications among lower extremity free flaps in our cohort, this finding was driven by the strong protective effect of two-vein outflow among muscle-based flaps. One-vein muscle flaps had 2.7 times higher risk of complications overall and a 12.8 times higher risk of partial flap failure. These results provide evidence for performing a second venous anastomosis when feasible, particularly among muscle flaps, for lower extremity trauma reconstruction.